As I was saying in my last column on Tuesday, what sane person would invest in a stock market like this? Who could stomach the wild swings up and down?

Stock prices plummeted yesterday mainly because professional investors suddenly snapped out of it, realizing that financial problems in Europe aren’t going to end just because Wall Street wants them to.

The truth is that the pros couldn’t keep a straight face any longer as they pretended that what was happening in Europe was good.

It’s not.

There’s nothing good about the change of leadership in Greece and especially Italy, where Prime Minister Silvio Berlusconi has agreed to leave that post after a new financial stability plan is approved.

Berlusconi, often a sideshow in the land of amoré, was the longest serving Italian PM since World War II.

And while that country is a mess, how is bringing in a newbie to the job going the make Italy’s debt situation any better?

I’d need to bump the sports section and abridge Page Six to list all the bad things going on in the world that the US stock market has been ignoring. Aside from Greece and Italy, France’s economy is souring. This shouldn’t shock anyone since President Nicolas Sarkozy has been talking recently like a guy under a lot of pressure.

And Europe’s problems won’t be contained just on that continent. American companies are already seeing their business slow because of weak foreign markets.

But wait, there’s more.

There’s Iran, which is closer than anyone thought to nuclear weapons. And there’s a rumor that the European Central Bank might need to call an emergency session.

And companies — think Japan’s Olympus — might not be totally honest with their earnings reports.

(That last one is the worst-kept secret of this generation of corporate leaders.)

Still more.

Mortgage delinquencies are rising in the US — with 5.88 percent of all homeowners late on payments in the June to September quarter, up from 5.82 percent in quarter two.

That, of course, means that there could be even more stress on banks that hold gobs of mortgages, not to mention Fannie Mae and Freddie Mac — the two organizations that have been sucking the blood out of the American taxpayer.

And don’t forget Bank of America, which not only wrote its own home loans but which also took over Countrywide Financial back in the bad ol’ days.

Traders, of course, aren’t going to take all this bad news sitting down. You can count on the fact that they will try to get stocks higher in the days ahead on any and all insignificant developments in Europe.

And that’s fine — this is what traders do. But you don’t have to play this game. Nope, what sane person would?

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This is belt — not to mention intestine — tightening!

Americans are forgoing beverages that cost money at restaurants and are drinking tap water instead.

The NPG Group, a research firm, says tap water servings increased by 2.8 billion since 2006. Other beverages are down 6 percent.

Are people really drinking water or supplementing their diets with microbes?

Over the past few weeks, my readers offered up Dumb Tax Ideas so we wouldn’t have to rely on Washington’s stupidity alone. Here’s another assignment for you.

What would you be willing to do to save a buck?

Please send me your responses ASAP.

I’m thinking of eating a lot more free bread in restaurants and then ordering off the kiddie menu.

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A report from the Consumer Federation of America says Wall Street speculation in energy futures is costing Americans $200 billion a year.

This amounts to 1 percent of the nation’s gross domestic product and almost 2 percent of all the money consumers spend.

The report goes by the snappy name Excessive Speculation and Oil Price Shock Recessions: A Case of Wall Street Déjà vu All Over Again.”

Mark Cooper, the CFA’s director of research, says the spike in oil prices between the summer of 2010 and 2011 was not caused by an increase in demand, which has been falling since 2005.

Even with demand going down, rising fuel prices are causing families to spend a record average of $2,900 a year to gas up their cars.

OK, I have two comments:

First, I’ve been trying to shed a light on this sort of Wall Street speculation for nearly six years. Now that everyone knows what’s going on, when is someone in Washington going to take action?

Second, can’t we outlaw the phrase “Déjà vu All Over Again?” It was cute when Yogi Berra said it; now it’s just tiresome.

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Why aren’t companies creating jobs?

Well, you can blame the rather exuberant stock market for that.

Let’s follow my cause and effect for this argument.

Corporate executives are basically out to protect their own interests. They are human (at least most of them are) and are, therefore, self centered.

And despite all the chaos in the world, the stock market has performed pretty well despite days like yesterday.

The people who run companies want their stock prices to remain high because they own a lot of equity in the outfits they run. And the only way to do that in this environment is to keep their company’s profits up.

Companies have reported good earnings — up 18 percent in the most recent quarter. In this stock market the surest way to hurt your stock price is to disappoint Wall Street on your earnings.

And the best way to cause profits to be disappointing is to start spending money. New workers cost money. And the Obama Care law makes the actual costs of hiring workers quite fuzzy.

So, let’s do that math: High stock market + executives’ desire to keep their stock prices up = refusal to hurt earnings by hiring expensive new workers. It really all adds up.